Molybdenum-Catalyzed Enantioselective Synthesis of Planar-Chiral (η⁵-Phosphacyclopentadienyl)manganese(I) Complexes and Application in Asymmetric Catalysis

Abstract

Enantioselective desymmetrization of C s -symmetric (η 5 -2,5-dialkenylphospholyl)(allyldiphenylphosphine)manganese(I) dicarbonyl complexes 1 was realized by molybdenum-catalyzed asymmetric ringclosing metathesis (ARCM), and the corresponding bridged planar-chiral phosphacymantrene derivatives 2 were obtained in good yields with excellent enantioselectivity. The enantioselectivity of the ARCM reaction was strongly influenced by the structures of the phospholyl-bound alkenyl groups, and the highest enantioselectivity of up to 99% ee was achieved in the reaction of 1d,e, which possess the 2-methylpropenyl substituents at the 2-and 5-positions of the η 5 -phospholides. Single-enantiomeric planarchiral 2d, which was obtained by the recrystallization of the highly enantiomerically enriched ARCM product, can serve as a chiral ligand for the palladium-catalyzed asymmetric allylic alkylation to show good enantioselectivity in up to 74% ee.

[​4+2] versus [​2+2] Homodimerization in P(V) Derivatives of 2,4-Disubstituted Phospholes

“…Leaving compound 6a in a standard NMR tube for several days exposed to natural light led to a good but not full conversion to the [2+2] head-to-head dimer 7a as shown by 31 P NMR. It has previously been shown that the coupling constant 1 J Se-P can provide information on the -donor ability of phospholes [4][5][6][7][29][30][31][32]. According to Table 5, phosphole 1b having the trimethylsilyl groups in positions 2 and 4 is the strongest -donor as 6b has the smallest coupling constant with 716 Hz, close to the value for 1phenyl-3,4-dimethylphosphole (713 Hz).…”

“…According to Table 5, phosphole 1b having the trimethylsilyl groups in positions 2 and 4 is the strongest -donor as 6b has the smallest coupling constant with 716 Hz, close to the value for 1phenyl-3,4-dimethylphosphole (713 Hz). The value for compound 6a is smaller compared to the corresponding 1,2,5triphenylselenooxophosphole (742 Hz) [4][5][6][7], indicating a certain influence of the position of the ring substituents on the -donor ability. Interestingly, the dimer 7a has a considerably higher coupling constant with 759 Hz.…”

“…Phospholes have found widespread interest in many areas, including catalysis, material sciences, and biological applications, due to the ready modification of their electronic, steric, and physicochemical properties and their different coordination modes to metals [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. Among the various possibilities, changing the substituents or the substitution pattern on the phosphole ring or on the phosphorus atom can modify the stability and the aromaticity of these heterocycles [15][16][17].…”

“…A major change is often induced by oxidation of the weakly aromatic P(III) compounds to non-or anti-aromatic P(V) derivatives employing oxygen/peroxides, sulphur, or selenium [18]. In material sciences and biological applications, the P(V) phospholes are mainly employed [8][9][10][11][12][13][14], whereas for catalysis and coordination chemistry purposes the P(III) heterocycles act as phosphine ligands or cyclopentadienyl analogues, or a combination of both [4][5][6][7].…”

Enantioselective Preparation of Planar‐Chiral Transition Metal Complexes by Asymmetric Olefin‐Metathesis Reactions in Metal Coordination Spheres

“…The enantioselective desymmetrization of C s ‐symmetric (η 5 ‐2,5‐dialkenylphospholyl)(allyldiphenylphosphine)manganese(I) dicarbonyl complexes 22 was realized by the molybdenum‐catalyzed ARCM, and the corresponding bridged planar‐chiral phosphacymantrene derivatives 23 were obtained in good yields with excellent enantioselectivity (Scheme 17). [33] Substrates 22 for this study possess an allylphosphine ligand and an η 5 ‐2,5‐bis(alkenyl)phospholide, where the two alkenyl substituents in the phospholide are identical and enantiotopic to each other. The enantioselectivity of the ARCM reaction was strongly influenced by the structures of the phospholyl‐bound alkenyl groups, and the highest enantioselectivity was achieved in the reaction of 22 e , which possesses the 2‐methylpropenyl substituents at the 2‐ and 5‐positions of the η 5 ‐phospholides, and ( R )‐ 23 e of 99 % ee was obtained in nearly quantitative yield.…”